Bursicon is the neuropeptide hormone that is responsible for hardening and darkening of the cuticle in insects.  It is one of the five key insect hormones which regulate the proper sequence of the insect molt.  Small amount of bursicon could be found in the brain.  It could be also detected in the ventral nerve cord 6-10 times more than in the brain.  The release time of bursicon is just after ecdysis at each molt.  The chemical structure of bursicon is a polypeptide of a single-chain molecule with a molecular weight of 30 kDa.  Additionally, nerve cord homogenates of several insect species and the lobster give results in the ligated fly bioassay.  These data indicate that bursicon has a conserved structure throughout arthropods.                 This article describes the bioassay, chemical identity and gene structure of bursicon.  Mode of action and application are discussed.